I hear you on that.
As a matter of interest, would an expectation of relatively clean image quality at ISO 1600 be unrealistic for a crop body?One man's clean is another man's filthy. It's best to speak in comparative terms. For me, if the 7D-II's ISO 3200 image looks as good as the 6D's ISO 6400 image then I'd be very happy with it.
As a birder, I dial in ISO 400 on my 500D but just like the 7D, anything over 400 leads to very obvious noise.
Anything over ISO 800, the images become somewhat and probably poorly described as rough.
Useable ISO 3200 would be a very worthwhile reason to buy this camera.
It's not going to happen, though. I agree, the most usable ISO stops somewhere around ISO 800 to ISO 1600 (depends on the specific copy, and to some degree temperature). The 7D has 41% Q.E. already. To DOUBLE sensitivity (or reduce noise by 50%), the 7D II would need 82% Q.E. Sony recently released the ICX694 CCD sensors for astrophotography. Those are cooled CCDs, about -35 to -40 degrees C delta T, and those get "only" get 77% Q.E. (which, BTW, is actually VERY high...the prior generation usually got somewhere between 45% - 59% Q.E. most of the time, with the exception of a couple high end ones without anti-blooming circuits that get 90%.) On top of that, they have the lowest read noise of any of the available astro CCDs on the market at the moment, at 0.003e-/px/s (the prior generation of CCD sensors had around 0.02e-/px/s, an order of magnitude MORE). DSLR sensors, at room temperature, has more on the order of 0.5e-/ps/s, another order of magnitude more.
There is just no way Canon is going to achieve 82% Q.E. in any respect (not unless they have some seriously amazing
patents they are hiding away somewhere), and there is little chance they will be reducing dark current noise by any significant degree. That means that the 7D II won't have anywhere near a factor of two improvement in high ISO noise. That means it won't even be that much more usable at ISO 1600, let alone ISO 3200.
If you really NEED usable high ISO, you need to move to a larger sensor. Total
light gathering capacity is ultimately what matters for high ISO...and FF sensors simply have more, always will have more.